FULL-WAVE SIMULATIONS OF SCATTERING IN VEGETATION FOR MICROWAVE REMOTE SENSING OF SOIL MOISTURE

The vegetation layer effects play an important role on microwave remote sensing of soil moisture. The classical Radiative Transfer Equation (RTE) and Distorted Born Approximation (DBA) model assume that the position of scatterers in vegetation is statistically homogeneous in 3D space. Such assumptions arc incorrect because the scatterers in vegetation are in clusters and also in the form of extended cylinders. In this paper, we develop a new hybrid method that makes the Numerical Maxwell Model of 3D (NMM3D) full-wave simulation possible for vegetation. A geometry setup is introduced to account for the gap effects and vegetation structure. The T-matrix of a single plant composed of multiple cylinders in a cluster is extracted using Huygen's principle and the vector cylindrical wave (VCW) expansions. Moldy-Lax multiple scattering (FL) equations are used to solve for the transmissivity of the vegetation layer. The convergence and accuracy of the hybrid method are verified using Ansys High Frequency Structure Simulator (HFSS). Transmission through wheat is calculated using the hybrid method and compared with those of RTE/DBA.